Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay
Ronald D. Stieglitz, M. Carol McCartneyand Paula E. Allen
On this field trip we will examine outcrops of Upper Ordovician and Silurianrocks along the face of the prominent escarpment on the east shore of GreenBay, and exposures of glacial materials, including the Two Creeks BuriedForest Bed, in eastern Wisconsin (Figure 1). The major objectives of thistrip are: (1) to examine some sections of glacial materials that are significant to working out the stratigraphy of the red tills in eastern Wisconsin,(2) to present some preliminary results of current research on the sedimentology of a portion of the Maquoketa Formation, and (3) to examine the glacialand post-glacial effects on the bedrock of the area as well as the reciprocalinfluence of the bedrock, particularly the Silurian escarpment, on the LateWisconsinan ice.
The bluffs which fringe much of the east shore of Green Bay are usuallyreferred, to as the Niagaran Escarpment, however, this designation is incorrect because they are formed of Lower Silurian, Alexandrian, strata in thisarea. The lowland to the west, containing the bay and the Fox River Valley,Is developed on the Maquoketa Formation and older Middle Ordovician dolomiteswest of the river. Tills, outwash and lacustrine clays overlie the bedrockand beach features are found at several elevations throughout the Valley.East of the bluffs, Alexandrian or Middle Silurian, Niagarian, strata formthe bedrock beneath glacial material of variable thickness.
Outcrops of the Maquoketa Formation are found along the shore of Green Bay as far north as the Little Sturgeon Bay area in Door County, Wisconsin, and in stream cuts and in quarries scattered throughout the. area west of the escarpment. No complete surface section of the Maquoketa Formation is known in the state, however, a complete section taken from a drill core at Oostburg In Sheboygan County is described by Froming (1971). One of the better exposures in this area, at Wequiock Falls, will be the first stop. The sequenceof shale, argillaceous dolomite and dolomite is abundantly fossiliferous anddisplays some interesting sediment-organism relationships.
The second stop will be at Bay Shore County Park in northern Brown County.A road cut to provide access to the bay shore exposes Alexandrian rocks andupper Maquoketa beds as well as the talus at the base of the escarpment.Features observable at this atop provide a transition from the Paleozoicpart of the trip to Pleistocene part by providing an opportunity to observethe effects of glacial and post-glacial conditions on the bedrock.The next part of the trip will focus on the Late Wisconsinan stratigraphy and history of eastern Wisconsin. After leaving the second stop we will drive south and east to the lake shore near Two Creeks. In so doing, we
Figure 1. Glacial geology of the Door County peninsula, from Hadley and Pelham(1976).
We will first pass across drift deposited by ice from the Green Bay Lobe andthen enter onto an area most recently covered by Lake Michigan Lobe ice.Four stops, two in Green Bay Lobe deposits and two in Lake Michigan Lobedeposits, are described here. We will not see all the red tills in eachlobe but we will see some of the typical relationships of the tills.Stop 3 at the lake shore exposure of the Two Creeks Forest Bed and thesucceeding Stop 4 at the Valders Quarry are both well known localities thatfigured prominently in the establishment of the stratigraphic and chronologic terminology applied to Lake Wisconsinan materials and events in theGreat Lakes region. The stratigraphic relationships between the two siteshave recently been reevaluated resulting in an as yet not totally acceptedrevision of the previous nomenclature (for a complete discussion see thepaper by McCartney elsewhere in this guidebook).
Stop 5 at the Brillion Quarry and Stop 6 at a pit east of De Pere providean introduction to the till stratigraphy of the eastern limb of the GreenBay Lobe and further evidence tearing on the revision of Late Wisconsinannomenclature.
The trip begins on the flood plain near the mouth of the Fox River. Subsurface borings for construction projects in the city have revealed that thechannel and mouth of the river have migrated widely over the valley in thepast. The route, primarily County Highway A, initially crosses flat, low-lying land along the southern and southeastern margin of Green Bay. Theentire area was submerged during glacial and post-glacial times. In thevicinity of the University campus prominent abandoned shoreline featurescan be seen. North of the campus, recent utility work exposed MaquoketaFormation, lake beds and till. Several sets of shorellnes have been mapped(Goldthwait, 1907), however, the exact timing of the events and water levelsstill require additional work for specific definition.
We will turn eastward at Van Lanen Road and cross an undulating area ofdrift and lake deposits which rise to the base of the Silurian Escarpment.Weather permitting, we will walk into the first stop and meet the buses atthe wayside. In the event of bad weather we will enter from the wayside.When we leave the first stop we will follow State Highway 57, which closelyfollows the edge of the escarpment, northward to the next stop at Bay ShoreCounty Park.
Fort Atkinson and Brainard members of the MaquoketaFormation; Alexandrian Strata. S 1/2, SW 1/4, Sec. 7, T24N, R22R, BrownCounty, Wisconsin. Green Bay East 75-mlnute Quadrangle.
The rocks of the Maquoketa Formation are generally easily eroded and lessresistant than the overlying Silurian dolomites and as a result form coveredslopes. This outcrop is one of the better and most accessible of thoseexposed as streams flowing over the escarpment cut away the most resistantSilurian beds. Weather permitting, we will traverse upstream and examinethe upper part of the Maquoketa Formation and the Mayville Dolomite (Figure 2)The Neda Formation is not present.
The traverse will begin in the uppermost part of the Fort Atkinson Member ofthe Maquoketa Formation which represents the last carbonate deposition beforethe Silurian. Hardgrounds which contain Spongll lomorpha type burrows and acoralline zone, that has yielded large stromatolltes, tabulate corals,coralline algae, horn corals, and numerous brachipods are present. The contact between the Fort Atkinson and the overlying Brainard Shale Member isalso exposed.
The Brainard Member is largely soft green mudstone but thin interbeds ofdolomitic shale and argillaceous dolomite containing brachiopods, arborescent bryozoans, cornulltes worm tubes, and occasionally stromatolltes arefound.80-
Figure 2. Generalized stratigraphic section at Wequiock Falls
About 2 meters of greenish-gray thin bedded dolomite lies above the mudstone. This unit forms the lower part of the steep valley walls just westof the bridge and the middle part of the face of the falls. The contactbetween the Maquoketa Formation and the Mayville Dolomite is tentativelyplaced below this unit. The top of the section is 3 to 4 meters of graymedium-to-coarse-grained dolomite characteristic of the Mayville Dolomite.
Alexandrian strata; Geomorphology of theSilurian Escarpment. NW 1/4, SW 1/4, Sec. 14, T25N, R22E, Brown County,Wisconsin, Dyckesville 75-Minute Quadrangle.
Alexandrian strata are exposed along a road cut through the escarpment toprovide access to boat launching facilities constructed on the bay shore.In this area the escarpment front is mantled by coarse talus and loosematerial which have also been truncated by the road. The parking lot andbreakwater at the base of the bluff are built on artificially filledmaterial. The grade of the road, although still steep, was lowered afterIts initial construction because of the difficulty of towing boat trailersback up the slope.
The free face of the bluff consists of about 105 meters of Mayville Dolomite which can be subdivided into three informal units (Figure 3). Theuppermost unit C capping the lip of the escarpment is, for the most part,light gray, fine-grained, thin-bedded dolomite. Some beds are very densewhereas others contain open vugs. The middle unit B is composed of dolomiteInterbedded with nodular layers of gray to black chert. The entire unitbreaks into small pieces and often has a fractured and rubbly appearance.
Figure 3. Generalized stratigraphic section at Bay Shore County Park.
It forms a reentrant in the cliff face. The lowermost unit A consists ofgray mostly fine-grained, thick-bedded dolomite. Some vugs and nodularlayers of chert are present.
Immediately below unit A a soft red clay several centimeters thick forms asmall reentrant. This material appears to be a thin representation of theNeda Formation.
The base of the bluff is mantled by talus, but in a few places less than ameter of greenish-gray, fine-grained, laminated dolomite outcrops. Thesebeds are dolomitic layers in the Brainard Member of the Maquoketa FormationThe layers show anomalous dips and appear to be slightly deformed perhapsby the movement of blocks of the overlying dolomite.
The effects of solution on the dolomite is evident both at the surfacebeneath the thin soil and along prominant joints. These features of thedolomite, well displayed at this location, graphically illustrate why thearea east of the escarpment is concerned about ground water pollution.
Figure 4. Relationships of the large blocks of Silurian dolomite to theescarpment, underlying rocks and talus.
Large blocks of dolomite, that have separated and moved away from the face ofthe escarpment are also visible (Figure 4). The blocks appear to have slidalong the surface of the underlying shale or argillaceous beds and may havebeen forced by ice wedging (Stieglitz, Moran and Harris, in press). Elsewhere in the park. In the picnic and camping areas, a series of open jointsare present which separate similar size block that remain in contact withthe escarpment face. The outermost of these blocks has moved down about ameter and a similar distance toward the bay shore. Back from the escarpmentedge several other open but narrower joints are present that separate blocksof similar width. Downslope adjustments of the blocks and coarse talus has produced what appear to be pressure ridges along the talus slope. The slopeis nearly stable and talus production and block movement may have occurredshortly after the last recession of the ice from the bay.
From Bay Shore Park we will turn right on Highway 57 and go about one mileto County Highway T where we will turn left (south). We will follow Highway T for about 20 miles to the city of Denmark. One mile south of Highway57 the road passes over a hill of Silurian dolomite. Glacial deposits areprimarily ground moraine from Green Bay Lobe ice.
Just south of the small community of Poland the topography becomes much morerugged and we will cross the Neshota River which is thought to be a glacialdrainageway which carried water to the southeast. We are traveling near themaximum southward and eastward extent of the Greatlakean ice of the Green BayLobe in the area as marked by the Denmark Moraine (Evenson and Mickelson,1974). The moraine complex near Denmark is the northern extension of theinterlobate moraine and is an older feature deposited between Green Bay Lobeand Lake Michigan Lobe ice during an earlier advance.
At Denmark we will turn onto Highway 141, cross the moraine and then turneast (left) onto County Highway BB. We will follow BB across Port Huronage Lake Michigan Lobe deposits onto younger Two Rivers Till near Stop 3 onthe lake shore.
Figure 5. Generalized stratigraphic section of the lake bluff at Stop 3north of Two Creeks, Wisconsin.
Significance: This locality is important because the dated forest bed(11,800 yrs BP, Broecker and Farrand, 1976) provides an absolute datefor late-glacial events in the Lake Michigan Basin. Thwaites and Bertrand (1957) correlated the upper red till here with the red till atValders. It is now believed that these tills do not correlate and thatthe Twocreekan was one of many retreat intervals which separated minorreadvances (Evenson and others. 1976).
From Stop 3 we will follow Highway 42 southward over Two Rivers till. Nearthe city of Two Rivers we will cross the Two Rivers Moraine and enter anarea of glacial lake sediments deposited in the lowlands of the Twin RiverYounger red till has not been found overlying the lacustrine sedimentssuggesting that post-Two Creekan ice did not cross the area.Just south of the city of Manitowoc we will turn west on State Highway 151following it, first across Lake Michigan Lobe drift of Port Huron age andthen over the Interlobate Moraine to Stop 4 at Valders.
Valders Till, unnamed till; Silurian dolomite. SW1/4, NW 1/4, Sec. 32, T19N, R23E, Manitowoc County, Wisconsin. Valders7 5-Minute Quadrangle.
This is also a well known and important site often mentioned in the literature (Figure 6). The bedrock here is Middle Silurian, Niagaran, inage. Directional indicators on the bedrock surface evidence two separateice flow directions.
Figure 6. Generalized stratigraphic section of the till relationships in the Valders Ouarrv.
Description: In parts of the quarry, the unnamed Middle Woodfordian age (Gary) till overlies the Silurian dolomite; in places the Late Woodfordian Valders till directly overlies the bedrock. Beneath the buff,sandy Middle Woodfordian till are striations on the dolomite whichtrend nearly north-south. Two sets of striations (north-south andeast-west) underlie the red, clayey Valders till. Cresentic gougeshave also been observed (Stieglitz, Moran and Quigley, 1978).
Significance: The striations indicate the ice advanced from the north anddeposited the sandy, unnamed till and that it later advanced from theeast and deposited the red Valders Till. Thwaites (1943) named theValders till for this locality and later (Thwaites and Bertrand, 1957)correlated it to the red till over the Two Creeks Forest Bed.
From Valders we will follow Highway 148 north to Highway 10. Weturn west and follow Highway 10 to the city of Brilllon. Duringof the trip we will return to an area covered by deposits laid down bythe east side of the Green Bay Lobe.
Chilton Till, Wayside Till; Silurian Dolomite.SW 1/4, SW 1/4, Sec. 24, T20N, R20E, Calumet County, Wisconsin, Brilliol7 5-Minute Quadrangle.
At this stop we will examine the stratigraphic relationships and characteristics of several tills overlying Silurian bedrock (Figure 7). The effectof the escarpment on ice flow will also be considered.
Description: There are two tills here on the dolomite bedrock. The lower till is the Wayside till; it is overlain by the Chilton till. The Wayside is the Middle Woodfordian sandy till and the Chilton is a LateWoodfordian clayey till. The sandy clay Branch River till, which liesbelow the Chilton till north of Brillion, is missing at this locality.
Figure 7. Generalized stratigraphic section of the till relationships in the Brilllon Quarry.
Significance: The ice that deposited the Chllton till during the late Woodfordian (late Port Huron) behaved differently than earlier or lateradvances. The ice extended further south than the early Port Huronadvance (which deposited the Branch River till) but did not extend asfar east or west in the northern portion of the lobe. Tee flow wascontrolled by the Niagara escarpment and ice left the lowland onlywhere the escarpment is very low. This suggests the ice had a lowerprofile than did ice of the preceding or succeeding advance. The lowerprofile may have been due to a higher water content at the bed.References: McCartney and Mickelson, in preparation.
From the Brillion Quarry we will follow Calumet and Brown County Highway PPnorth to State Highway 32. After traveling less than a mile on Highway 32we will turn eastward (right) on Sportsman Drive and follow several townroads to County Highway X where we will turn east (right) to Stop 6.The route northward roughly parallels the Silurian Escarpment which lies tothe west. The highway passes over the edge of the escarpment near HillyHaven Golf Course and crosses a small sediment filled reentrant. From thisarea to the pit at Stop 6 we will be traveling on unconsolidated materialdeposited along the west face of the escarpment.
Glenmore Till over Chilton Till,separated by dated Two Creekan Forest Bed; outwash deposits. Southeastedge of French Grant 38, Northwest corner, T22N, R21E, Brown County, Wisconsin, De Pere 75-Mlnute Quadrangle.
At this site we will examine several tills and thick outwash deposited alongthe face of the Silurian Escarpment (Figure 8). The outwash is highly dissected by streams flowing off the escarpment toward the northwest. The pitexposes channels, cross-bedding and large fault blocks of sand and gravel.Part of the pit is being filled by paper mill sludge. Directly across Highway X to the south is the Brown County East Landfill site.
Figure 8. Generalized stratigraphic section of the buried forest andthe till relationships at the Scray Hill pit.References: Kessenich, pers. comm., 1976McCartney and Mickelson, in preparation,Mickelson and Evenson, 1975
Created 25 July 2001, Last Update 13 January 2020
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